Conventional steel-making techniques often call for taking the molten metal of an initial steel melt and pouring it into large molds so as to cast giant ingots. These ingots can then be easily shipped and/or stored as desired. Later, the ingots are remelted and the steel obtained therefrom utilized in specific manufacturing operations.
For obvious reasons, it is generally preferred that the giant ingots be formed substantially free of large voids. Now it is well known in the industry that large voids will tend to appear in the ingots if premature solidification of the melt is allowed to take place about the upper edges of the mold while the melt in the center of the mold is still molten. As a result, steps are usually taken to stop this premature solidification. The most common method of preventing such premature solidification is to apply a liner of suitable insulation, generally available in the industry in board-like lengths under such names as Hot-Top, Riser, etc., to the upper inside portion of the mold. This insulation then acts to retard heat loss through the mold at its upper end, thereby assuring that the melt will not prematurely freeze on the mold.
There are currently two different types of ingot molds in common use in the steel industry, and the method and means for attaching the insulation liner to the upper inside portion of the mold differs somewhat depending on the type of mold being used.
The first type of mold in common use is a mold of the type which is open at its top end and closed off at its bottom end by a base plate. The vertical walls of the mold are of singular construction and may be disposed so that the mold has a uniform cross-section along its height. Alternatively, the walls of the mold may be tapered so that its interior cross-section changes linearly with height. In this type of ingot mold the layer of insulation is attached to the upper inside surfaces of the mold for a relatively short distance down from the top end of the mold. Various methods and means for attaching the insulation boards to the mold are well known in the art and are described and illustrated in such U.S. Pat. Nos. as: 3,436,883, 4,131,262, 3,797,801, 3,966,167, 3,506,236, 4,083,528, 3,722,848, and 3,002,238.
The second type of ingot mold now in common use, and the one which we are concerned with here, is comprised of two parts. A first part, the mold body, is substantially like the mold described above, i.e. it comprises a structure which is open at its top end and closed off at its bottom end by a base plate. The mold walls may or may not be tapered with height. A second part of the mold, the mold cap, is of similar structure, but it is much shorter in length and open on both ends. It also may or may not have its vertical walls tapered with height. The mold cap is sized and shaped so that it can sit atop the mold body and form a top extension therefore. As a result, when the mold cap and the mold body are properly united to form the complete mold unit, they are together capable of producing a single ingot.
With this second type of ingot mold, the liner of insulation is applied only to the mold cap and not to the mold body. To this end the mold cap is lifted up from its position atop the mold body and inverted so that its lower end (i.e. that end which contacted the mold body when the cap sat atop the body) is made to face upwards. Then the cap is lowered to the ground with this inverted orientation. Next workmen cover the cap's interior surfaces with insulation boards and also part of the cap's now-exposed lower end. The insulation boards are generally held onto the mold cap by large C-shaped wire clips which fit over (and run between) the two ends of the cap so that the insulation boards are captivated between the wire clips and the mold cap. Once the insulation boards have been affixed to the cap via the wire clips, the cap is lifted off the ground, inverted once more so that it reassumes its original orientation (with the now partially-insulated lower end once again facing downward) and then reseated atop the mold body. In this way the two parts of the mold are reunited so as to constitute the complete ingot mold, with the complete ingot mold being lined about its upper inside end with a layer of insulation so that the mold is capable of forming substantially void-free ingots.
Unfortunately, such an arrangement for applying the liner of insulation to the two-piece ingot mold is not entirely satisfactory. In particular, it has been found that the C-shaped wire clips generally used to hold the insulation boards on the cap sometimes slip out of place during the lifting and reinverting of the cap. (In this respect it is to be appreciated that the mold caps are generally quite heavy, typically weighing several tons apiece, and the action of lifting and reinverting the cap can sometimes be quite violent). As a result, the insulation boards can come free from the cap and may fail to form the requisite insulating liner for the cap. This means that the insulation boards must be re-attached to the mold in a time-consuming procedure or, if the insulation detachment goes unnoticed as is often the case, one runs the substantial risk that the ingot produced may have large voids therein.